1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device suitably applicable to engine mounts, body mounts or other mounts for use in automotive vehicles, for example.
2. Description of the Related Art
In automotive vehicles each having an engine as a vibrational source, an engine mount has been used for supporting the engine on a body frame of the vehicle in a vibration isolating fashion. FIG. 8 shows an example of such an engine mount in the form of a fluid-filled vibration-damping device.
The known fluid-filled vibration damping device includes: a first mounting member 101 of shaft configuration; a rubber elastic body 102 bonded at one end to the first mounting member and having a recess 123 open in the other end; a second mounting member 103 of cylindrical configuration bonded on an outer circumferential surface of the other end of the elastic body 102; a diaphragm whose peripheral portion is supported by an inner circumferential surface of the second mounting member 103 so that the diaphragm 104 cooperates with the elastic body 102 to define therebetween a fluid chamber 145 filled with a fluid “L”; and a partition member 105 whose peripheral portion is supported by the inner circumferential surface of the second mounting member 103 so that the partition member 105 divides the fluid chamber 145 into a primary fluid chamber 146 and an auxiliary fluid chamber 147. The partition member 105 consists of: a metallic orifice-defining member 151 adapted to define an orifice passage 154 for fluid communication between the primary and auxiliary fluid chambers 146, 147; and a movable rubber plate 152 disposed in a central hole formed through the orifice-defining member 151.
This fluid-filled vibration damping device is installed on the vehicle such that the first mounting member 101 is fixed to a mounting portion on one side of a body and an engine by means of a mounting bolt (not shown), and the second mounting member 103 is press-fitted into a mounting portion on the other side of the body and engine. With the fluid-filled vibration-damping device thus installed on the vehicle, the fluid chamber 146 may be located upward or downward in a direction in which a primary vibrational load is applied to the device.
The thus installed fluid-filled vibration damping device is able to absorb high frequency vibrational loads based on elastic deformation of the elastic body 102 and engine shakes or other low frequency vibrational loads based on resonance of fluid flowing through the orifice passage 154 caused by a fluid pressure variation and a volumetric change excited in the primary fluid chamber 146 and the auxiliary fluid chamber 147. This fluid pressure variation between these chambers 146 and 147 may be suitably regulated by means of the movable rubber plate 152 of the partition member 105.
During operation of the known fluid-filled vibration-damping device, the fluid L is forced to flow within the fluid chamber 145 based on the fluid-pressure variation in the fluid chamber 145. In this condition, oxygen dissolved in the fluid L is prone to be vaporized, causing generation of a multiplicity of bubbles within the fluid L. Especially in the primary fluid chamber, these bubbles are more likely to be generated, since the fluid pressure variation is made larger in the primary fluid chamber than the other part of the fluid chamber 145. Upon application of a vibrational load to the fluid-filled vibration-damping device, these bubbles are likely to be generated and burst repeatedly in the fluid L. When bursting, these bubbles generate impact that is exerted on the surface of the orifice-defining member exposed to the fluid chamber 145. As a result, the impact of the bubble bursting may be undesirably transmitted as noises to a vehicle room, possibly causing deterioration in silence in the vehicle room and driving comfort as felt by a driver or passengers.